(DATA)CLAIREPARKINSON/NASAGODDARDSPACEFLIGHTCENTERANDNICKDIGIROLAMO/SSAIsuggest that global warming should beeroding sea ice around Antarctica. Themodels are “totally missing it,” says SharonStammerjohn, an oceanographer at theUniversity of Colorado in Boulder and aleader of the expedition.The fate of Antarctica’s sea ice has globalimplications. The ice reflects the sun’s rays,a planet-cooling effect thought to have asmuch impact on climate as the warmingcaused by greenhouse gases from humanactivities. As surface seawater freezes,salt is expelled, making the water belowdenser and prone to sinking, which helpsdrive bottom currents that distribute heataround the planet. The sea ice is also hometo algae that nourish tiny crustaceansknown as krill, a cornerstone of the South-ern Ocean’s bountiful populations of fish,birds, seals, and whales.To improve forecasts, the re-searchers aim to visit severalRoss Sea regions believed to playkey roles in the sea ice life cycle.One target is swathes of openwater near the coastline, knownas polynyas (derived from a Rus-sian word for a natural hole inthe ice). Polynyas act as ice ma-chines, churning out new ice thatis pushed out to sea by intensewinds, keeping the water openand exposed to cold air, which inturn creates more ice. Further outto sea, the researchers will planta constellation of buoys atop theice, which will operate through thewinter, collecting detailed tem-perature and weather data as wellas making measurements that aredifficult for orbiting sensors, suchas the massof the ice. The Palmer’screw also will launch a roboticsubmarine and aerial drones ableto create detailed maps of both ice sheetsurfaces and undersides.A leading candidate for explaining whatis happening in the Ross is a regionalweather pattern known as the AmundsenSea low. Researchers believe changes in thelocation and intensity of the low have beenbringing warmer winds from the northinto the Bellingshausen and Amundsenseas, helping melt ice there. The changesalso produce more cold, dry winds blow-ing across the Ross Sea, contributing to thecreation of polynas.But Raphael says the icy winds scenario“doesn’t seem to explain all” that’s occur-ring in the Ross. Other forces also couldbe at work, such as an increase in fresh-water from melting ice shelves, whichfreezes more easily than salt water, orchanges in ocean temperatures or cur-rents. To piece together these potentialfactors, the Palmer plans to collect a bevyof measurements as ice is being con-ceived in two of the sea’s main polynyas.Stammerjohn hopes the visits will coincidewith one of the fierce, days-long storms,driven by powerful katabatic winds fallingfrom the continent. “We’ll see some prettystrong extremes,” she predicts.Marika Holland, a sea ice modeler at theNational Center for Atmospheric Researchin Boulder, will welcome any data on polyn-yas. Their poorly understood behavior, shesays, could be a source of shortcomings inclimate models. “We’ve been trying to under-stand polynya dynamics,” she says, so datafrom the cruise “is going to be really helpful.”But ice also forms far from the polynyas,within the Ross Sea pack itself, as snow ac-cumulates and as some ice is twisted andcrushed together. That’s why the expedi-tion also aims to stop in several offshoreareas and deploy the buoys and drones.The overall goal is to assemble a detailed,3D view of the ice pack as it evolvesthrough the winter, says Ted Maksym, asea ice physicist at the Woods Hole Ocean-ographic Institution in Massachusetts, andone of the expedition’s lead scientists.It’s not yet clear how much ice will greetthe researchers when they reach the RossSea later this month. Given the Antarcticpack’s general expansion in recent decades,observers were surprised when the extent ofice in the Ross Sea and elsewhere in Antarc-tica precipitously shrank last year.The plunge served as a reminder of howmuch we still don’t know about sea icedynamics, Holland says. The Palmer ex-pedition could help scientists understandwhether the downturn was just anotherswing in a natural pendulum, or an earlysign of a human-driven melt that couldhave global significance. j10111213

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Antarctic Arctic

Diverging paths

The extent of average annual sea ice around Antarctica has
increased, in part because of gains in the Ross Sea, even as the
Arctic ice pack has shrunk.